1. Field of the Invention
The present disclosure relates to a transparent oxide with p-type having semiconductivity which can be used as active semiconductor devices such as TFT-LCD and transparent solar cell and a manufacture method of the same, particularly relates to TFT (Thin Film Transistor) of p-type transparent oxide semiconductor with new composition featured by remarkably superior properties such as visible light transmittance (T), carrier mobility (μ), and rectification ratio, and manufacture method of the same.
2. Background of the Invention
Although amorphous silicon (Si) is mainly used in the TFT (Thin Film Transistor) used for electric device currently, it has some disadvantages that switching speed is slow due to low carrier mobility and high temperature process is required in manufacturing thin film, compared with oxide semiconductor.
In addition, optical devices applying optical function need development of TFT (Thin Film Transistor) using a new p-type transparent oxide because of restrictions such as opacity caused by small band-gap originally possessed by the amorphous silicon.
Amorphous transparent oxide semiconductor (TOS) is capable of low temperature process, advantageous to epitaxy due to very low surface roughness from small particle size, and proper to micro-patterning including lithography process. Therefore, amorphous InGaO3 (ZnO)5 (IGZO) series n-type channel materials (mobility at RT: >10 cm2/Vs) has been developed and used as a part of TFT materials, until now. In order to manufacture active devices on flexible substrates such as semiconductor (inverters etc.), optical device (LED, LD etc.), and solar cell, it is required to develop of p-type oxide materials with excellent electric property of amorphous phase even at low temperature.
In the TFT development history, the oxide TFT announced by Phillips Research Institute in 1995 was a memory device manufactured by applying SnO2 ferroelectrics as gate dielectrics, which was the beginning of oxide TFT related studies. Then, when using InGaO3(ZnO)5 material published by Hosono et al, Tokyo Institute of Technology, Japan as TFT channel, a device with 80 cm2/Vs of mobility and 105 of Ion/off ratio was obtained [Hosono, et al, Science, 300, p1269 (2003)]. However, this device had a problem to need high temperature heat treatment over 1400° C. The reason that this device had very rapid mobility in spite of amorphous film was reported that overlap of s-orbital wavefunction having smallest anisotrophy according to metal valence electron direction in the oxide contributed to band charge transfer of election.
Since the results of Hosono et al., researches to obtain a new p-type semiconductor material has been progressed, but in the most cases of them, vacuum equipment was used during the process to manufacture the oxide semiconductor. Although in this method, low temperature process was possible, it had still a disadvantage to use an expensive equipment. Therefore, it is clear helpful to cost reduction to manufacture oxide semiconductor TFT using solution process.
Recently, some research groups has manufactured thin films through sol-gel method, MOD (metal organic decomposition method), nano-particle dispersion solution method, and chemical bath deposition (CBD) after preparing precursor at first.
For the solution using precursor, it is possible to vary its crystallinity and mobility using one component, two component, and three component system. For instance, Chang et al., Oregon State University, US realized high mobility as much as 30 cm2/Vs with printing method. However, in this case there was a disadvantage that high off current (Ioff) was not solved [Chang, et, al., J. Mater. Chem., 19, p. 3135 (2009)].
Like these, for materialization of TFT, the most researches has been based on organic semiconductor using solution process and the organic semiconductor TFT has been the first candidate as a next generation flexible display driving device for the last 10 years. However, the organic semiconductor TFT still has not solved difficult problems in terms of mobility, current density, confidence, and manufacturing process.
On the contrary, in case of the sol-gel oxide semiconductor process, its post heat treatment temperature is still higher in spite of several advantages and it is known that 500˜600° C. of temperature is required in manufacturing ZnO thin film alone. As the sol-gel method is a process to form an inorganic network through hydrolysis of precursors at appropriate pH, coat a substrate with a solution containing the above, and then produce metal oxide through post heat treatment, main ingredients of pre-polymerized colloid phase are ceramic precursors, so it leaves room for lowering heat treatment temperature. In this case, metal alkoxide or metal acetate is commonly used as a precursor and the precursor compound should have high solubility, maintain stable solution-phase, and produce little amount of precipitate after heat treatment.
The sol coating consists of dip coating, spin coating, and spray coating and some cases to apply the sol for manufacturing an oxide semiconductor by ink-jet printing has been reported. For instance, Moon et al., manufactured sol-gel solution for Zn,Sn Oxide (ZTO) to use it as an ink for ink-jet, where the transistor manufactured by printing ZTO (Sn: 30 mol %) solution between source electrode and drain electrode obtained 0.01 cm2/Vs of mobility and 105 of on/off current ratio. [J. H. Moon, et al., J. Phys. Chem. C, 112, p. 11082 (2008)]. In this case, although post heat treatment was performed at 500° C. by preparing sol-gel solution with 2-methoxyethanol and stabilizing agent by using zinc acetate dehydrate and tin acetate as source, it was determined that its mobility was low. Therefore on the basis of ZTO of which process was improved, a result that the mobility was improved to 0.1˜0.5 cm2/Vs by measuring TFT property after heat treatment at 350˜500° C. was published. Besides, another case to manufacture TFT through high temperature heat treatment after dip-coating or spin-coating of Zn1-xMgxO and Zn1-xZrO sol gel solution for preparing a thin film was reported. Recently, a result to form Zn0.97Zr0.03O thin film with sol-gel method at 300° C., relatively lower temperature as process temperature for TFT and demonstrate 4.1 inch QVGA TFT-LCD using this was published also and in this case, it was found that although Zinc acetate and zirconium propoxide were used as precursors, it resulted in properties such as 0.0042 cm2/Vs of mobility and 24.5V of Vth.
Because most oxide semiconductors which has been known until now shows n-type properties, if a transparent oxide semiconductor with p-type properties is materialized, it will be possible to manufacture CMOS type transparent electronic devices and there will be a lot of advantages for driving of OLED. Therefore, a research to seek p-type transparent oxide semiconductor material for transparent TFT devices is necessary.